Electrical tools are presently being used in industrial manufacture and maintenance instead of manual tools. For example, an electrical wrench is used to fasten work pieces such as bolts or nuts. Sometimes during operation, a work piece can be locked when the electrical wrench tightens the work piece in an positive direction but it cannot be disassembled when the electrical wrench releases the work piece in a negative direction. The reason is that, when the electrical wrench is used to tighten the work piece, the output is changed from a high-speed state to stop state and thus a relatively large impacting torque is generated so as to tighten the work piece; but, when disassembling the work piece, the output is in a stalled state at the beginning, and the starting torque is relatively small, thus it is difficult to twist the work piece free.
At present, in order to resolve the above problem, a mechanical impacting assembly is added to the electrical wrench. The conventional impacting assembly comprises a hammer and an anvil, wherein the hammer is supported onto a spindle by a rolling ball arranged in a groove, and the anvil is driven by convex portions correspondingly arranged on the hammer and the anvil for generating an output. When the rotation of the anvil is blocked by resistance, the hammer will move axially backwards relative to the spindle against an elastic member arranged on the rear end of the hammer, and then the convex portions on the hammer and the anvil are staggered and restored rotatably under the biasing action of the elastic member, thus the convex portions on the hammer and the anvil come into contact again and an impacting action is generated. If the rotation of the anvil is blocked by resistance continuously, the above process is repeated so as to perform a continuous impacting action.
Arranging a mechanical impacting assembly in an electrical wrench may add to the number of members required in manufacture. Moreover, due to the continuous impacting action, there are high requirements for the mechanical accuracy and strength of the members. Thus, the electrical wrench provided with the mechanical impacting assembly greatly increases the manufacturing cost. In addition, the mechanical assembly may cause mechanical wear and damage on the device, thus the impacting efficiency will be decreased after a long time of operation and even the failure of the impacting action can occurred, thereby reducing the working life of the electrical wrench.